Expandable conveyors are widely and conventionally employed to convey items such as corrugated containers of product in warehouses, manufacturing facilities and other locations. For example, expandable conveyors may be employed at the terminus of conveyor branches in a warehousing rigid and fixed conveyor distribution system to extend from the branches of the central conveyor system in flexible fashion in order to accommodate various trucks and shipping containers. The conveyors may be moved, for instance, back and forth, left and right in order to accommodate the locations in which a truck is parked and to direct the stream of items to the particular portion of the truck being filled.
Expandable conveyors often take the form of scissors or "lazy tongs" structures. These conventionally contain a pair of scissor structures which act as expandable load bearing members spanned by a plurality of elongated rollers. The members forming the scissors structures are usually connected at substantially their top and bottom portions and their mid-portions to each other to provide proper linkage, expandability and strength. Various connections may be omitted, such as mid-point connections, for manufacturing efficiency and other purposes.
Such expandable roller conveyors are disclosed in, for instance, U.S. Pat. No. 4,852,712 issued Aug. 1, 1989 to Best entitled "Conveyor" which discloses an extensible lazy tong conveyor. U.S. Pat. No. 5,147,025 issued Sep. 15, 1992 to Flippo, entitled "Expandable Powered Roller Conveyor" discloses powered expandable conveyors featuring a drive motor and one or more belts or chains connected to the drive motor and to multiple rows of skate wheels or elongated rollers. U.S. Pat. No. 5,224,584 issued Jul. 6, 1993 to Best, et al., entitled "Expandable Powered Conveyors" discloses powered conveyors in which the power unit is located external to the rollers and connected to them via a number of chains or belts. U.S. patent application Ser. No. 08/022,012 to Best, et al. filed Feb. 24, 1993, entitled "Controllably Powered Roller Conveyors" discloses powered lazy tong conveyors in which the power units are located within, or internally of, the rollers. All of these patent documents are incorporated herein by this reference.
The configurations disclosed in U.S. Pat. Nos. 5,147,025 and 5,224,584 mentioned above employ lengthy drive belts or chains which engage a motor sprocket or pulley and connect to a number of rows of skate wheels or elongated rollers. Among other things, a belt or chain failure subjects the entire conveyor to a power failure. Furthermore, such a power transmission means can preclude segmenting the conveyor into a number of independently powered zones so that accumulation techniques may be employed. However, such configurations are preferable to the extent they use large, conventional drive motors mounted external to the rollers; the motors are easily accessible, more durable and less expensive than smaller motors such as ones inside the rollers.
U.S. patent application Ser. No. 08/022,012 mentioned above discloses another approach: that of expandable conveyors in which the rollers feature internal motors. This approach allows individual control over power applied to each motorized roller simply by changing the electrical power to the roller. It allows, accordingly, creation of independently actuable and controllable power zones so that accumulation techniques may be employed. However, the smaller, internal motors are expensive, less reliable, and more difficult to maintain than external motors of the type mentioned in U.S. Pat. Nos. 5,147,025 and 5,224,584.